Hot-wire electric meter.



NQ. 7l5,l70. Patented Dec. 2, l19H32.

R. S. STEWART. HOT WIRE ELECTRIC METER. Application led Apr. 28, 19027.)

(No Model.)

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UNITED STATES PATENT OFFICE..

ROBERT STUART STEWART, OF DETROIT, MICHIGAN.

HOT-WIRE ELECTRIC METER.

SPECIFICATION forming part of Letters Patent No. 715,170, dated December 2, 1902- Application filed April 26, 1902.

To all whom, it may concern: I

Be it known that I, ROBERT STUART STEW- ART, acitizen of the United States, and a reisident of Detroit, in the county of lVayne and State of Michigan, have invented a new and.

Improved Hot-Wire Elect-ric Meter, of'which the following is a full, clear, and exact description.

My invention relates to a meter for making electrical measurements'of various kinds and capable of use as a voltmeter, differential voltineter, ammeter, rc., according io the materials used in its construction and the proportion of the parts. It is also capable of use with both alternating and direct currents.

Reference is to be had to the accompanying drawings, forming a part of this specication, in which similar characters of reference indicate corresponding parts in all the figures.

Figure 1 is a side elevation of my device complete. Fig. 2 is a diagram in perspective of the Working parts of the meter, and Fig. 3 is a horizontal section upon the line x of Fig. 1.

Upon the base 1 are mounted verticalstandards 2 3, upon the tops of which is secured a plate 4, provided with binding-posts 5 6 6a 7. To these binding-posts are electrically con# nected posts 8 9 9 10, to which the wires 11 14 and 12 13 are fastened.

1l 14 constitute one continuous wire, and 12 13 another of the same length. These wires may either be threaded through eyes 16 17 in the bar 18 or may be fastened to the bar in any appropriate manner. 1t is preferable for many uses of the instrument that the two Wires be electrically insulated from The bar 18 may be of any shape suitable and may be made of any non-magnetic substance. Its uses are to hold the wires in a xed definite shape and to carry a pointer by which any deection from its original position maybe measured on a scale provided for this purpose. A horizontal disk 19 is provided with graduations 2O 21 and secured at the points 22 23 upon the standards 2 3, the bar 18 being suspended immediately over this disk 19. The bar 1S may be steadied by the vertical Wire 23 and slightly tensioned, if desired, bythe spring 24: and adjusting- For delicate measurements the pointer maybe replaced by a small mirror and the deflections read by optical means. In order that the wires may be'kept under serial no.' 104,777. (nu moda.)

some tension, the bar 13,l is madeofsome weight, or for portable instruments the spring 24 is fastened to the center of the bar.

The four posts S, 9, 9a, and 10 are on the circumference of a circle at the ends of diameters which are at right angles to each other. The diameter of this circle will ordinarily be equal to the length of the bar 1S, but this is not necessary. All deflections of the bar are in a horizontal plane.

Operation of the instrument-To measure an electric current, the circuit is connected to the binding-posts 5 and 7. The current to be measured will then pass through the wire 1 1 14, and this wire will expand by an amount proportional to .the square of the current due to the heating effect. As thewire 12 13 has no current flowing through it, its length will remain unchanged and the bar 18 will take a newA position in the horizontal planein which it lies. This deiection of thebar from its original position is a measure of the increase in the length of the wire 11 14, and consequently of the square of the current flowing in the wire 11 14. To measure the dierence between two currents, I connect one circuit to the posts 5 and 7 and the other to the posts 6 and 6a. One current will then iiow through the wire 11 14 and the other through the wire 12 13. IE the two currents are equal, the two wires will expand by equal amounts and there will be no deflection; but if one current is greater than the other the deiiection will measure the difference in the squares of the two currents.v

Theory of the 'instrument-Let us call the length of the wires 1l 12 13 14 each equal to 1, the length of the bar between the two Wires equal to N, the distance between 8 and 10 and 9 and Qaalso equal to N, the increase in the length of the wires 11 andV 14 due to expansion equalA to d', and the angle through which the bar is deflected due to this expansion equal to X. We then have the relation d N2 d 1T I S1110 E T l the percentage of expansion and isV proportional to the sine of the angle of deflection, being a constant for the in- IOO rent, the expression for the value of the current is sine fr,

C@ CH2 In these equations the weight oi the bar, tension of the spring, and surrounding temperature do not enter, and the results are therefore independent of these quantities. The

N constant which is a measure of the sensibility of the instrument, indicates that we can increase the sensibility either by decreasing the length of the bar or increasing the length of theA Wires.

Friction does not affect the instrument in any Way, for there are no pivots or sliding contacts to cause friction. The measurements are not affected by proximity to magnets.

Y By suitable choice of the material of which the wires are made and by the use of the customary resistances the apparatus can be built for a Voltmeter, ammeter, differential Voltmeter, or synchroscope for paralleling alter-- nators. In this last capacity it indicates when the voltages, phases, and frequency of the two machines are the same by a single zero reading.

Having thus described my invention, I claim as new and desire to secure by Letters 4o Patent- 1. A hot-Wire electric meter, comprising a frame, two wires suspended therefrom, a pointer fastened to said wires and free to deiiect when the length of said wires is changed, means for measuring the defiections of said pointer, and electrical connections for sending electric currents through either or both of said wires for the purpose of heating the same.

2. A hot-wire electric meter, comprising a frame, two biilar suspensions attached to said frame and fastened to a single pointer, and so adjusted with respect to each other that 'any change in the length of either suspension will cause a deection of said pointer, said bifilar suspensionsbeing composed of wires of conducting material and so arranged that an electric current may be passed through either or both of said biiilar suspensions for the purpose of heating the same.

3. The combination of two bilarsuspensions, composed of wires of electric-conducting material so arranged as to exert equal and opposite forces upon asingle pointer attached to both said suspensions, electrical connections by which electric currents may be passed through either or both of said bifilar suspensions, thereby heating and changing.

the length of either or both said bi'ilar suspensions, and so altering the forces acting on the pointer that they will cause it to take a new position in space.

In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses.

ROBERT STUART STEWART. 

